memoized-getter-define.ts

/**
 * Defines a getter on a specified object that will be created upon first use.
 *
 * https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/XPCOMUtils.jsm#defineLazyGetter()
 * https://dxr.mozilla.org/mozilla-central/source/js/xpconnect/loader/XPCOMUtils.jsm#120
 */
function defineMemoizedGetter(object: any, prop: string, fn: Function) {
	let redefining = false

	Object.defineProperty(object, prop, {
		get: function() {
			if (!redefining) {
				// Make sure we don't get into an infinite recursion loop
				redefining = true

				const value = fn.apply(object)

				Object.defineProperty(object, prop, {
					configurable: true,
					enumerable: true,
					value,
					writable: true
				})

				return value
			}
		},
		configurable: true,
		enumerable: true
	})
}